Inside Vietnam’s incredible underground wonderland

Vietnam is home to some of the world’s most extraordinary subterranean landscapes. Here we highlight some striking new images of the caves of Quảng Bình province on the north-central coast, taken for Oxalis Adventure Tours.

Son Doong

Two large rivers – the Khe Ry and Rao Thuong – join to form the Son Doong cave, the world’s largest cave passage.

Large enough to fit an entire New York City block with 40-storey skyscrapers, the 9km cave system is up to 200 metres high and 160 metres wide, which is big enough for a Boeing 747 to fly through.

The massive cave system is so huge that it has its own climate, with mist and clouds forming and rising up from inside.

The cave features two skylights, formed after its ceiling collapsed hundreds of thousands of years ago. The giant openings allow plenty of sunlight into the cave, giving life to a lush tropical jungle (complete with large trees, palms and ferns) within.

Its surreal interior also houses a 90m-high calcite wall known as The Great Wall of Vietnam, which visitors can climb, using ropes and supported by safety harnesses.

Son Doong lies beneath Phong Nha-Kẻ Bàng National Park and is nearly three million years old, but was only explored properly in 2009, with the help of the British Caving Association.

Oxalis, a Vietnamese adventure travel company, is the only tour operator to offer trips into the caves.

Hang Va

This lesser known cave discovered by a team of British cavers in 2012 sits close to the village of Phong Nha and is not too far from the Ho Chi Minh Highway.

Spanning a length of 1.6 kilometres, the cave features calcite towers rising up to two metres high from waters held back by calcite dams.

Just how the unusual rock formations of the Raft Cone Chamber are created remains a mystery.

Hang Va is a habitat for blind white fish and blind white freshwater prawns, both of which have adapted to living in a dark environment.

Many small bats have also made a home in the small stream passage.

A trek through rocky jungle terrain brings visitors to the small valley where Hang Va is located and visitors can camp there by night.

Tu Lan

Stretching for 20 kilometres, this incredible place is made of 20 caves, 10 of which can be visited at the moment.

Its longest cave is the 3.7km Hang Ken, which has both a wet passage and a dry passage, while Hang Song Oxalis is notable for its fantastic display of cave coral patches.

Visitors can swim through underground river caves with remarkable calcite formations, especially in the dry caves.

You might also recognise the area around these caves from last year’s Kong: Skull Island, the Hollywood film starring Tom Hiddleston and Samuel L Jackson which was shot there.

Hang Tien

At 100 metres high and 50 metres wide, Hang Tien is the biggest cave of the Tu Lan system and features a beautiful blue natural pool.

Thrillseekers can ‘fly’ across it using its newly installed ‘flying fox’ crossing system, equipped with harnesses and steel cables.

Also known as the Fairy Cave, it houses various rock formations, large passages and is made of multi-layered limestone, which gives its walls a stripy appearance.

During the summer, Hang Tien is a dry cave while in the wet season a huge river flows through it.

A bat colony resides in the highest part of the cave.

For more information on tours of these caves, see oxalis.com.vn.

By RYAN DEBOODT (The Telegraph)